Since the discovery of photography in the first half of the nineteenth century, numerous and varied methods of printing photographic images on solid surfaces have been developed and employed. In all these methods, the image is formed by the application to a smooth and photographically unvariegated surface a layer of pigment or other colorant in such a manner that of the light striking the surface at any given location, the amount that is reflected, is inversely proportional to the amount of colorant at that location, and the distribution of said colorant on the surface corresponds to the shadows, midtones, and highlights of the photographic image. Except in the cases where a photo-sensitive emulsion is applied to the surface and subsequently exposed and developed, and in screen printing, all these methods utilize the transference, in one or more stages, of the colorant from the surface of a printing plate or matrix that predetermines the final distribution of said colorant, to the surface of the final object. Except in the photo-chemical processes, Woodbury-type, dye transfer, and, to a lesser extent, photogravure, all of the methods employ a nearly uniform film of colorant that is distributed in a minute pattern of dots, the size and proximity of which control the reflectivity of any given location in the image. This pattern of dots is called a half-tone screen.
In the now-obsolete Woodburytype process, a photographic relief is made by exposing thick, photo-sensitive dichromated gelatin film to an actinic light source through a continuous-tone, photographic negative. After washing out the unexposed portions of the gelatin with hot water and drying, the result is a relief image in tough, insoluble gelatin, thick in the shadow areas and progressively thinner in the midtones and highlights. An intaglio printing mold is made by forcing an impression of said relief into a lead plate in a hydraulic press. This mold is then filled with warm pigmented gelatin solution and a sheet of prepared paper is laid over it. A platen is then brought down over all. This forces the gelatin into the corners and interstices of the mold and surface of the paper and the excess gelatin out along the sides. When the gelatin is cooled and jelled, the paper is removed from the mold and allowed to dry. When dry the pigmented gelatin forms a tough film on the surface of the paper that is thicker and darker in the shadows and progressively thinner and lighter in the midtones through the highlights.
Photo-polymers are synthetic materials that harden and become solid and/or insoluble on exposure to light. They are used to make flexographic printing plates, rubber stamps, and molds for casting plaques and similar items. When exposed to light they harden away from the exposed surface so the greater the exposure is, the thicker the hardened area. Photo-polymer processes use high contrast litho film that, after exposing and developing has opaque areas and clear areas; it does not have shaded or gray areas. When a photo-polymer is exposed through one of these high contrast films it only hardens under the areas in the film that are clear, creating a non-continuous-tone, photographic relief. Photogravure and rotogravure are the only other known processes which use continuous-tone film to produce a continuous-tone relief, both of which use either a grained or screened pattern which tends to break the image up into dots, similar to the half-tone processes, and both transfer the colorant, in these cases ink, from the intaglio relief onto a separate substrate to produce the final object.
Ceramists and potters have long known that indentations and variations in ceramic surfaces affect the depth and color of overlying glazes. They have utilized this property in the decoration of their manufactures by incising, carving and impressing patterns and designs on the surfaces of the clays and molds, which are brought out and enhanced by the types and manner of application of glazes. There are fine Danish plates that have delicate hand carved intaglio images pressed into their surfaces and filled with a blue glaze that appear to be individually hand painted.
Basse-taille, a beautiful, jewel-like enameling, often done on silver, utilizes the same principle with a finely sculpted surface underlying a translucent enamel glaze.
No known photo-chemical or photo-mechanical printing techniques utilize a glaze-filled, continuous-tone relief as the final image. Only gravure and Woodburytype utilize varying the thickness of the colorant to control reflectivity, and they are both transfer processes: the intaglio relief that determines the thickness of the layer of colorant is a type of printing plate, a means to an end, not the final object. No known glazing or enameling techniques utilize a photographically formed continuous-tone underlying relief.
The previously unattempted combination of a photographically formed, continuous-tone relief filled with a translucent glaze determines the thickness or depth of the colorant or glaze by the depth of the relief in the surface of the final object itself. This creates a beautiful, continuous-tone photographic image which, depending upon the materials used, can be extremely durable and colorfast as well.